Seat # ______Chemistry 153AWinter 2000Final ExamKEYQuestion #Value Score1302273184145296107138129 81021111812 4013 1014 1515 1216 23TOTAL 300TOTAL COURSESCOREFINAL COURSEGRADESeat # ______First letter of your last name ________________KEY_______________Print your full name(Last Name First)______________________________Print your TA's name______________________________Time and day of your discussion sectionI have read the instructions below.______________________________SignatureINSTRUCTIONSREAD EACH QUESTION CAREFULLY!SHOW YOUR CALCULATIONS!WRITE YOUR LAST NAME IN THE SPACEPROVIDED ON EVERY PAGE OF THE EXAM.NO CREDIT WILL BE GIVEN FOR ANYTHINGWRITTEN ON THE BACK OF A PAGE OR IN ASPACE OTHER THAN THAT PROVIDED FORYOUR ANSWER.ANSWERS MUST BE BRIEF AND TO THEPOINT. WHERE WORD LIMITS ARE GIVEN,NO CREDIT WILL BE GIVEN FOR ANY PARTOF YOUR ANSWER THAT SIGNIFICANTLYEXCEEDS THAT LIMIT.Numbers in parentheses represent the point values.∆∆∆∆Go’ of ATP hydrolysis = -30.5 kJ/mole Gas constant: R= 8.31 x 10-3 kJ/ K/mole2.3RT = 5.7 kJ/mole for std. cond. or 5.9 kJ/mole for biol. cond.Faraday’s constant: 96.5 kJ V-1 mol-1Name______KEY_____________________11. (30) a. (5) You make a solution by adding 0.220 moles of A-, the conjugate base of a weak acid, HA (pKa=6) to pure water. Youadjust the final pH of the solution to precisely pH 5 and bring the total volume to 1 liter by addition of more water.What is the molar concentration of each of the following species in this solution?H+___10-5______ M OH_____10-9_____ MA-___0.020____ M HA ___0.200_____ MH2O___55.5_____ Mb. (2) Which do you expect to have a greater effect on the pH of the above solution, the addition of 20 millimoles of HCl orthe addition of 20 millimoles of NaOH. ____HCl___________c. (2) Based on your answer to b above, write an equation representing the reaction responsible for the change in pH.HCl + H2O →→→→ H3O+ + Cl-d. (10) Complete the following drawing of L--methionyl-L-histidinyl--L-asparagine in the form that would predominate at pH 9.Show the stereochemistry of the α-carbons by using appropriate wedge shaped and dashed bonds to each side chain andto each α−hydrogen. There is no need to show any stereochemistry within the side chains.H2NCCNCCNCCOOCH2HCH2HCH2HHHOOCCH2SCH3NNHONH2e. (8) Draw a titration curve (pH vs. H+ equiv.) for the peptide in d above using standard pka’s given in the compendium.H+ equivalents0.5 1.0 1.5 2.0 2.5 3.02468101214pH3.5 4.0f. (3) Calculate the isoelectric point for this tripeptide.pI = (6+8)/2 = 7Name______KEY_____________________22. (27) a. (5) Consider glycine and β-alanine whose structures are shown below.COOCHH3NHCOOCCHHHH3NH1) Is either of these compounds optically active (i.e. do they have stereoisomers)? _No___ If so, which? __NA_____2) Which of these compounds do you expect to have the higher pka for deprotonation of its carboxyl group? ββββ-alanine3) Which is a protein amino acid? __glycine___b. The instructor of your analytical chemistry laboratory course gives you a test tube and tells you it contains a pure solutionof alanine that has been purified from a base hydrolysate of an alanine rich protein. You determine that the compound inthe solution indeed has two ionizable groups having pKa’s consistent with the α-amino and α-carboxyl groups of alanine.You perform other tests which confirm that the remaining two substituents of the α-carbon are a hydrogen and a methylgroup. You then place a sample of the solution at pH 7 in a polarimeter to observe the rotation of plane polarized lightand find that there is no net rotation of light in either direction.1) Briefly describe how you determined that the compound had two ionizable groups with the expected pKa’s. [≤50 words]I brought a sample at known concentration to pH 1, and titrated by gradual addition of OH- while constantlymonitoring the pH. The two pKa’s can be detected as the pH’s at the midpoints of buffering zones whichoccur at 0.5 and 1.5 equivalents of OH-. (Could also be done by starting at high pH and titrating with H+.)2) Taking into account how the alanine sample was obtained, give the most plausible explanation for the lack ofobservable optical activity in the polarimeter experiment. [≤25 words]It is a racemic mixtute of D & L isomers of alanine, due to racemization in the base hydrolysis.c. Arrange the following protein amino acids from left to right in order of increasing pKa for ionization of side chain.arginine, aspartic acid, cysteine, histidine, lysineaspartic acid, histidine, cysteine, lysine, arginine d. Match each of the following terms on the left with the one phrase that best describes it with reference to proteins.Letter Term Description Dbackbone atoms A. amide bondGpeptide plate B.. depends entirely on ionic interactionsApeptide bond C. largely entropy drivenFsecondary structure D. everything except the side chainsEnative conformation E. tertiary structure in single polypeptide proteinsChydrophobic effect F. primarily stabilized by hydrogen bondsG. does not include α-hydrogens and side chainse. Match each of the following amino acids on the left with the one on the right with which it will have the most stable sidechain interaction at pH 7.Letter Term DescriptionClysine A. valineDaspartate B. cysteineAleucine C. glutamateBcysteine D. arginineName______KEY_____________________33. (18) You have discovered a new protein. You wish to determine its primary sequence in your own laboratory before makingyour discovery known. You do not have the facilities necessary for Edman degradation, but you do have the capability tocarry out N-terminal analysis, enzyme proteolysis, acid hydrolysis, and amino acid analysis. The results of yourexperimental procedures and analysis are as follows:Treatment of the intact polypeptide hormone with DANSYL Chloride produced the two following dansylated products ina ratio of 2 to 1.NCH3CH3SOOHNCHCOOHNCH3CH3SOOHNCHCH2COOHC H2H2 CC H2H2 CNH32: NHH N 1Treatment of the protein with carboxypeptidase A, which cleaves all C-terminal residues except pro, lys, and arg, had noeffect. Three separate samples of the polypeptide were treated with trypsin, chymotrypsin and cyanogen bromide. Theresulting fragments were acid hydrolyzed, and amino acid analysis yielded the following data. Amino acid compositionof each fragment is presented in alphabetical order and does not suggest the order of amino acid
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